Electrical submersible pumps are commonly used in oil and gas wells for producing large volumes of production fluid. An electrical submersible pump (hereinafter referred to “ESP”) normally has a centrifugal pump with a large number of stages of impellers and diffusers. The pump is driven by a downhole motor, which is a large three-phase motor. A seal section separates the motor from the pump to equalise the internal pressure of lubricant within the motor to the pressure of the well bore. Often, additional components will be included, such as a gas separator, a sand separator and a pressure and temperature measuring module.
An ESP is normally installed by securing it to a string of production tubing and lowering the ESP assembly into the well. Production tubing is made up of sections of pipe, each being about 30 feet in length. The well will be ‘dead’, that is not be capable of flowing under its own pressure, while the pump and tubing are lowered into the well. To prevent the possibility of a blowout, a kill fluid may be loaded in the well, the kill fluid having a weight that provides a hydrostatic pressure significantly greater than that of the formation pressure.
In normal operations it is desirable to access the reservoir below the ESP to perform a production log to determine where the different fluids are flowing from and perform treatments using coiled tubing to either stimulate a section of reservoir or seal a section of the reservoir producing too much water.
Coiled tubing has been used for a number of years for deploying various tools in wells, including wells that are live. A pressure controller, often referred to as a stripper and blowout preventer, is mounted at the upper end of the well to seal around the coiled tubing while the coiled tubing is moving into or out of the well. The coiled tubing comprises steel tubing that wraps around a large reel. An injector grips the coiled tubing and forces it from the reel into the well.